Integrally capacitively ballasted discharge lamp



ep 1953 M. e. CLARKE ET AL 4 INTEGRALLY CAPACITIVELY BALLASTED DISCHARGE LAMP Filed July 12, 1950 Inven'h'ors: Maurice Georg CLarke. Herbefl" Lawrence Prive-t't, y M l fi Their Ak't'orneg.

Patented Sept. 29, 1953 INTEGRALLY CAPACITIVELY BALLASTED DISCHARGE LAMP Maurice G. Clarke, Church Lawford, and Herbert Privett, Rugby, Warwick, England, assignors to General Electric Company, a corporation of New York Application July 12, 1950, Serial No. 173,326 In Great Britain July 29, 1949 8 Claims.

The present invention relates to gaseous electric devices generally and more particularly to devices of the kind in which there is produced a discharge having a negative volt-ampere characteristic. The invention is concerned with an improved construction, integral with the device or lamp, which converts the inherent negative volt-ampere characteristic of the discharge to a resultant positive volt-ampere characteristic for the device as a whole. This permits operation of the lamp directly from an alternating voltage source without the use of external ballasting impedances.

Discharge devices of the character mentioned above are used for many various purposes and appear in diiferent forms, among which may be mentioned discharge lamps of the low pressure and high pressure types and the common tubular fluorescent lamps. In order to limit the current in such lamps and insure satisfactory operation, a positive impedance is inserted in series therewith across a source of voltage. Where the voltage supply is alternating, the impedance is generally in the form of a reactance, as otherwise an unnecessary wastage of electrical energy would occur. This reactance is usually of an inductive nature for normal supply frequencies, and it is generally not feasible to employ a reactance of a capacitive nature because of the deterioration of wave-form which occurs. However, where the frequency of the alternating supply is materially higher than the commercial frequencies of 50 to 60' cycles, for example a frequency of 200 cycles per second or more, the ballasting reactance may be capacitive in nature; and the wave-form of the current, and also the emciency of the lamp, remain satisfactory.

Accordingly, it is an object of the invention to provide a new and improved electric discharge device in which series capacitance is used for stabilizing the operation and inwhich the capacitance is constructed integrally with the device.

Another object of the invention is to provide a discharge lamp construction wherein the inherent negative volt-ampere characteristic of the discharge is countered by the positive voltampere characteristic of a capacitance of which the dielectric is constituted by a part of the envelope wall of the device, the whole providing a resultant volt-ampere characteristic which is positive in nature.

A further object of the invention is to provide a discharge lamp construction wherein capacitive ballasting is achieved by utilizing a transparent conductive coating and an insulating glaze on the envelope wall as capacitive elements in combination with the ionizable medium Within the lamp;

In general, the invention providesa capacitance integral with the discharge device in the form of a conductive coating on the Wall of the envelope of the device and surrounding substantially the whole of the discharge space. The coating is separated from the discharge space by dielectric material, either the envelope wall or a. separate insulating glaze, and forms one terminal of the device while an electrode immersed in the ionizable medium forms the other terminal. As an example, the envelope may be coated. externally with a conductive light-transmitting coating forming one side or plate of a series ballasting capacitance. The other plate of the capacitance may be either a second conductive light-transmitting film deposited internally on the envelope wall, or the ionized medium of the discharge itself enclosed within the envelope. In the case of a lamp provided with an internally deposited film or coating, a connection may be made from this coating to a dischargesupporting electrode within the envelope, which electrode cooperates with a second electrode at the opposite end of the path of the discharge within the device. In the case of the lamp where the ionized medium of the discharge itself forms the other side or plate of the capacitance, only one discharge-suporting electrode is necessary within the envelope.

For further objects and advantages and for a better understanding of the invention, attention is now directed to the following description and accompanying drawings. The features of the invention believed to be novel will be more particularly pointed out in the appended claims.

In the drawings:

Fig. 1 is a pictorial view of a tubular elongated discharge lamp which is provided integrally with a series ballasting capacitance whereof the plates are formed by external and internal translucent or transparent coatings on the envelope wall.

Fig. 2 is a sectional view of an elongated discharge lamp provided with an integrally constructed ballasting capacitance whereof one plate is formed by a transparent coating on the exterior wall of the envelope and whereof the other plate is constituted by the ionized medium of the discharge itself.

Fig. 3 is a sectional view of a discharge lamp of standard pear-shaped bulb construction which is provided with a series ballasting capacitance whereof one conducting plate is constituted by a transparent conductive coating located between the interior surface of the envelope wall and a thin translucent dielectric glaze deposited on the inner surface.

Referring to Fig. 1, there is shown a discharge lamp I embodying myinvention. whichexternal and internal conductive coatings are provided on the envelope wall, the internal coating being connected to one of a pair oi dischargesupporting electrodes. The lamp is represented as broken apart near its middle in:..order to 1 18. cilitate the understanding of its construction.'-.. The lamp comprises an elongated tubular. ens velope 2 which is terminated at"both=ends' in. stem presses 3 and 4, stem ..3being.further pro? vided with an exhaust tube 3 for'evacuating the envelope and introducing suitable gases therein. Mounted on lead-in wires passing through-the stem presses are filamentary electrode'sfiand-3," which electrodes may consist of a coil ot-tungsten wire overlaid with a coating of activated electron-emitting material such as barium and. strontium oxides. The electrodeilea'd-in' wires" are connectedto pairs of pins. .I and'fl'fixed in suitable moldedbases at bothends' of thellarnp.

The glass wall of the envelope! is coated both' externally and internally with light transmitting conductive coatings 9 and'lfl; respectively. As is well known'in the'art, a transparent conductive coating may be. formed by the application of stannous chloride to the glass. Or again, translucentcoatingmay be formed by the sublimation onto theglass-surfa'ce of certain metals. For in stancaaluminum maybe usedto provide aconductive light-transmitting film. The internal conductivecoatingnldis connected "to one side of electrode 5 .by means .,of.a spring finger ll. mounted phone. of theflead-iri. wires.

I'nits finalgassemblywhere the lamp is to be v utilizedto produce-visible.'light,.a thin layer ii of a fiuorescentsubstance isdeposited on the internal surface oil the .envelopeover. .the' internalv conductive translucent. coating. The function of. this, fluorescent. coating. isto convert the ultra violet radiation producedby. the dischargeto light radiation .within the visible spectrum. After as-.- sembly, thelamp is evacuated, filled-with a starting gas such asneon, .argon,. krypton,. xenon, or mixtures thereof at a low pressure. inlth'eneigh borhood of 3 mm-.. In addition, a dropletof'men. 45 cury I3 is introduced into the bulb which during. normal op,eration,.fills theenvelope with its vapor pressure at the operating temperature, such vapor pressurebeingin the .range of a few microns.

Lamp 1, constructed as described above, may be operated directly from an alternating voltage source at the usually accepted voltage.of'200' to .v 250 volts and preferably at a frequency in" excess of 50 cyclesper second, for instance, a' frequency of 200cycles per second. Where itis'de; 55 sired to operate the lamp from a sourceof lower voltage, means may ,be providedforsupplying heating current. to the. filamentary. electrodes. 5" and 6. Such means may be, for instance, atransformer l5 whereof the primary I6 is connected across the alternating voltage supply. terminals. l4, and .whereofithe secondary windings l1. and" 18 are connected across the filamentary electrodes.

andt, respectively. The.actualioperatingcircuit for the lamp is provided inthe same manner as. where. the electrodes are not .prleheated, by means of a direct connection lafrom the-external conductive coating B toone of the alternating voltage terminals, andby means of 'a' direct connection 20' from one side of'filamentary electrode 6 to the other alternating voltageterminal.

Referring to Fig.2, there is shown a discharge. lamp 22*embodying a modified form of jmy in vention in which an external conductive coating alone is utilized and in which the ionizable medium itself within the envelope is utilized as the other plate of the ballasting capacitance. Mounted atone end of envelope 2 is a-single stem press 3 supporting the filamentary electrode 5.

- The opposite end of the envelope is simply sealed off. Conductive coating 9 is deposited on the exterionwall' of the envelope and serves as one plate' or the ballasting capacitance. In operation, one lead-in wire to electrode 5 has a direct connection 23 to one-terminal of the alternating voltage-supply and the conductive coating 9 has a direct connection to the other terminal of the alternatingvoltage supply. With this construction; the'discharge medium within the envel'ope' serves as the other plate of the series capacitanegand current limiting is achieved directly through the ballasting effect of the capacitance so constituted;

Referring to- Fig. 3, there' is shown a pear shaped discharge lamp construction-embodying a furthermodifica'tion-oi my invention. Where the frequency -of-the alternating-supply voltage is relatively low and it isynevertheless, desired to ob tain a relatively'intehise discharge, the value of the :integral ballasting zicapacitance" may be increased'byreducing the thickness ofthe' diele'c tric: Of course, it is not possibletd decrease iridefinitelyi the: thickness of the glass envelope since 1 extreme fragility is'undsirable; butthiS' difficulty may be obviated by the use of-a dielectric skin or'layer on 'one' surface of'the main'glass envelope; Thus;-in'the pear-shaped-lanip 301 the interiorsurface of=the glass-envelope 3| is-coated surface of the glazed coating 33. -In such case,- the interior of the envelope 3 l wouldbe evacuated I and'filled with 'a starting gas and, preferably; a metal-vapor such as mercury. Onthe other hand, when a gas such-as neon, which produces visible radiation directly, is utilized; thefiuorescent powder may be-omitted: The lamp is-pro-' vided'with asingle electrode 34 whichmay be constituted bya coilof tungsten wire activated with electron-emittingmaterials such as stronti um -or barium oxides. The eIectrodeM-is'supported on a lead-in wire which is connected to the central pin 35-ofa screw base 36:" The conductive coating which is locatedbetween "the exterior glass envelope-and the internal glazeis connected by "means of-a metal ring-Hand a lead=" in wire-38 tothe bod-y of the screw base? i The lamp 30 may be screwed in directly to the usual type of standard screw socketon'a'commerical -supplyof-approximately 230 volts at cycles. With this construction, the thickness of the-dielectric constituted bythe glazebetween" the conductive coating and the 'ionizable medium is so smallthat the series capacitance has a'high enoughivalueto conduct suiiicient current to per-- mit the generation of commercially utilizable light. manner as. described heretofore, by means of the positive resistance characteristic of---the integral capacitance in series with'the discharge.

While certainspecific embodiments have" been shown and described, it will' ofcoursebe under stood that various modifications may be made without departing from the invention. Thus, the

The ballasting is achievedyin-the same a shape and sizes of lamps which have been described and also the types of cathodes may be changed and, likewise, the dimensions and the particular operating circuits. It will be understood that those which have been described are shown merely by Way of illustrative examples. The appended claims are therefore intended to cover any such modifications coming Within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A self-ballasting construction for an electric discharge device wherein the discharge proper has a negative volt-ampere characteristic, comprising an envelope filled with an ionizable medium and defining a. discharge space, at least one lead wire sealed through said envelope and supporting therein a thermionic activated electrode, and a series ballasting capacitance constructed integrally with said device and comprising a conductive coating on the wall of said envelope and surrounding substantially the whole of said discharge space, a dielectric material separating said coating from said medium, said lead and said conductive coating serving respectively as terminals for said device whereat a resultant positive volt-ampere characteristic is presented.

2. A self-ballasting construction for an electric discharge lamp wherein the discharge proper has a negative volt-ampere characteristic, comprising a dielectric envelope filled with an ionizable medium, at least one lead wire sealed through said envelope and supporting therein a thermionic activated electrode, and a ballasting capacitance constructed integrally with said lamp and comprising an external electrically conductive and light-transmitting coating covering substantially the whole outside surface of said envelope, said coating being adapted to react capacitively through the walls of said envelope operating as a dielectric, said lead and said external coating serving respectively as terminals for said lamp whereat a resultant positive volt-ampere characteristic is presented.

3. A self-ballasting construction for an electric discharge device wherein the discharge proper has a negative volt-ampere characteristic, comprising a dielectric envelope filled with an ionizable medium, a pair of cooperating thermionic activated electrodes positioned at opposite ends of said envelope and supported on lead wires sealed therethrough, and a ballasting capacitance constructed integrally with said device and comprising external and internal conductive coatings covering substantially the whole outside and inside surfaces of said envelope, said coatings, in conjunction with said dielectric envelope, constituting a capacitance, and a connection from one of said electrodes to said internal coating, the lead to the other of said electrodes and said external coating serving respectively as terminals for said lamp whereat a resultant positive voltampere characteristic is presented.

4. A self -ballasting construction for an electric discharge lamp wherein the discharge proper has a negative volt-ampere characteristic, comprising a transparent dielectric envelope filled with an ionizable medium, a pair of cooperating thermionic activated electrodes positioned at opposite ends of said envelope and supported on lead wires sealed therethrough, and a series ballasting capacitance constructed integrally with said lamp and comprising external and internal electrically conductive light-transmitting coatings covering substantially the whole outside and inside surfaces of said envelope, said coatings, iii conjunction with the wall of said envelope serving as a dielectric, constituting a capacitance, and a connection from one of said electrodes to said internal coating, the lead to said other electrode and said external coating serving respectively as terminals for said lamp whereat a resultant positive volt-ampere characteristic is presented to an applied alternating voltage.

5. A self-ballasting construction for an electric discharge lamp wherein the discharge proper has a negative volt-ampere characteristic, comprising a transparent dielectric envelope having a pair of activated thermionic electrodes positioned at opposite ends thereof and supported on lead wires sealed therethrough, a starting gas at a low pressure of a few millimeters of mercury and a small quantity of mercury sealed within said envelope, and a series ballasting capacitance constructed integrally with said lamp, and comprising external and internal electrically conductive lighttransmitting coatings covering substantially the Whole outside and inside surfaces, respectively, of said envelope, said coatings constituting, in conjunction with the dielectric of said envelope, a capacitance, and a connection from said internal coating to one of said electrodes, the lead to said other electrode and said external coating serving respectively as terminals for said lamp Whereat a resultant positive volt-ampere characteristic is presented to an applied alternating voltage capable of producing a discharge within said lamp.

6. A discharge device construction as in claim 1 wherein the envelope is a dielectric and the conductive coating is light transmitting and is placed on the outside surface of the envelope so as to react capacitively upon the ionizable medium through the envelope wall.

7. A discharge device construction as in claim 1 wherein the conductive coating is light transmitting and is placed on the inside surface of the envelope, and comprising in addition a, dielectric glaze within said envelope covering said coating, said glaze serving as a dielectric between said coating and the ionizable medium.

8. A discharge device construction as in claim 1 wherein the conductive coating is light transmitting and is placed on the inside surface of the envelope, and comprising in addition a translucent dielectric glaze inside said envelope covering said conductive coating, said glaze serving as a dielectric between said coating and the ionizable medium, and a phosphor within said envelope deposited over said glaze.

MAURICE G. CLARKE. HERBERT L. PRIVE'I'I'.

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